Titanium powder for commercial use is presently produced by a hydride-dehydride (HDH) process, as disclosed in U.S. Pat. No. 6,168,644, by gas atomization, or by the plasma-rotating electrode process, as disclosed in U.S. Pat. No. 6,136,060. Raw materials for HDH process are titanium metal obtained by re-melting and processing titanium sponge, or ready-crushed titanium sponge itself. These raw materials are hydrogenated; then, the brittle hydrogenated titanium is ground to the desired powder size that is dehydrogenated by vacuum heating. Essentially, the titanium powder production is a multi-step, energy-consumable, high-cost industrial process including the manufacture of titanium sponge, which is the most expensive part of the technology.
Numerous disclosures for magnesium-reducing TiCl4 and subsequent processing of the obtained titanium sponge are present in the art, starting from U.S. Pat. No. 2,205,854 granted to Wilhelm Kroll in 1940. Most developments were directed to improve the quality of the sponge by diminishing the final content of magnesium, chlorine, oxygen, and iron contaminants. Various processes have been developed during the last two decades for energy-saving, cost-effective, sponge-related technologies.
The manufacture of titanium powder from reduced titanium sponge or sponge-like product includes (a) magnesium-thermic reduction of titanium chlorides in a reactor, (b) preliminary distillation of the reaction mass to the content of magnesium chloride of 5-12%, (c) cooling of the obtained sponge block in argon, (d) crushing and grinding the sponge into the powder having a particle size of 0-12 mm, (e) preliminary drying of the powder at <250° C., (f) cooling and additional grinding, (g) final distillation of the powder from magnesium chloride residues by vacuum separation, (h) hydro-metallurgical treatment, (i) final drying, and (j) final grinding of the titanium powder.
In spite of saving time and energy in sponge production, this process is not cost-effective when considering titanium powder as the final product. In this process, the first stage of vacuum separation is carried out at 1020° C., which results in a solid sintered block of the reaction mass and increases the time of sponge distillation. Double-stage vacuum separation accompanied by multi-stage drying and grinding increases the process time and electric energy consumption, and significantly decreases the powder productivity. Besides, multi-stage hot drying increases the content of gaseous impurities in the obtained powder.
Periodic removal of exhaust magnesium chloride from the reactor bottom and cooling a reaction interface by argon flow reduced the time of sponge production, but neither the cost nor the energy of the entire process of powder manufacture is gained.
The same result, insignificant to powder cost, was reached in the process disclosed in JP 61012836, 1986 which increases the sponge yield by predetermined blowing of TiCl4 at the temperature of <600° C. under argon into molten magnesium.
The electric power consumption was decreased by 20% using a condensing vessel in the reactor for removing unreacted magnesium and residual magnesium chloride from the reaction zone. This energy savings related only to sponge production and does not reflect on the total production cost because the obtained ductile sponge needs to be hydrated/dehydrated with the repetition of the multi-stage processing.
Productivity of the magnesium-thermic process was increased by the preliminary cleaning of TiCl4 and accelerated the supply into the reactor. This method also related only to the sponge production and results mostly in the sponge quality.
A way of accelerating the distillation stage was offered also. According to this, the oxide impurities are partially soluble in fused MgCl2 at a higher temperature, therefore the reduction process should be carried out at more elevated temperature and simultaneously increase feeding the reactor with TiCl4 to obtain a porous titanium sponge, which facilitates the removal of fused MgCl2 together with oxygen dissolved in it. Unfortunately, the higher temperature results in additional power consumption.
The supply of hot argon through the reaction mass can also speed up the distillation process by vaporizing the magnesium and magnesium chloride in gaseous form, as disclosed in the U.S. Pat. No. 3,880,652. But additional expenses involved with heating and supplying high-temperature argon override the savings on production cost during the distillation stage.
The titanium powder according to the U.S. Pat. No. 6,638,336 granted to Drozdenko et al. is manufactured by (a) magnesium-thermic reduction of titanium chlorides characterized by the formation of a hollow block of the reaction mass having an open cavity in the center of the block, (b) thermal-vacuum separation of the hollow block from excessive Mg and MgCl2 at 850-950° C., (c) cooling of the obtained titanium hollow block in a H2-contained atmosphere at an excessive hydrogen pressure, (d) crushing and grinding the hydrogenated titanium block, and (e) hydro-metallurgical treatment of obtained titanium powder in a diluted aqueous solution of at least one chloride selected from magnesium chloride, sodium chloride, potassium chloride, or titanium chloride. The hydro-metallurgical treatment of titanium powder significantly increases labor and time of the process, but however does not provide the desirable purity of the powder which contains magnesium and chlorine contaminants up to 1%.
The manufacture of high-purity titanium sponge lumps includes crushing the titanium sponge to a particle size of 2-50 mm and heat-treating at a reduced argon pressure of 600-1100° C. Crushing and heat treatment are repeated several times until the desired purity of coarse titanium is reached. This method is ineffective for commonly used titanium, and requires HDH processing to obtain the powder for industrial purposes.
All other known methods of producing titanium powder directly from magnesium-reduced sponge or sponge-like porous titanium compound have the same drawback: cost and energy savings are only realized for one or two stages, but not for the continuous multi-stage process, which makes none of these processes cost-effective.
Not one conventional process comprises the sponge or sponge-like hydrogenated porous titanium compound production adjusted specially to subsequent powder manufacture: sponge lumps are ductile and need to be treated by HDH process.
Also, all processes known from the prior art do not provide high productivity together with the sufficient purification of the hydrogenated titanium compound within one production cycle. All products require additional purification (either by hydration-dehydration or hydrometallurgical treatment) in order to remove impurities, especially magnesium and magnesium chloride to the concentration below 1 wt. %.